1. Field of the Invention
The present invention simplifies and renders practical the control of hydrostatic transmissions in which the pumps, with either impelling or motor functions, are preferably of the rotational type and of infinitely variable debit of fluid, so that the variation of the said debit may be automatic, according to the variation of the pressure in the fluid circuit of the transmission. The said pumps have an internal stator 2, which is decentralised in axial way, between the rotor 1 and the box or external stator 3 by means of the rods A and B.
A fundamental characteristic of the said pumps is the fact that the variable work pressures of the fluid, which act on the internal side of the stator 2, are compensated and balanced on the corresponding external side by equal fluid pressures.
2. Description of the Related Art
In the previous hydrostatic transmissions of the rotational type and of variable debit, a great obstacle has been the great strength that is necessary to be applied in the impulsion of the internal stator in order to be obtained the variation of the amplitude and direction of its decentralisation.
The said impulsion is opposed by the work pressures of the fluid, which are produced in the internal side of the stator and which are opposed to the said variation due to the fact that they are not balanced by equal pressures on the external and opposed side.
As a consequence, it is necessary to have impulsion systems based on xe2x80x9cscrew systemsxe2x80x9d or based on the hydrostatic systems of a great strength and of a very complicated construction.
In short, there are several negative facts in the previous types of hydrostatic transmissions:xe2x80x94lack of compensation and balance of the work pressures between the internal and the external sides of the movable stator;xe2x80x94excessive number of devices with heavy weight and high obstruction;xe2x80x94complicated and slow control;xe2x80x94the variation of the fluid debit does not automatically respond to the pressure variation generated in the proper transmission circuit, resulting from the variation of its work load.
These negative facts have been preventing its application in numerous work situations for hydrostatic transmissions.
For instance, in the hydrostatic transmission type described in the Document U.S. Pat. No. 3,354,637 A (CROSWHITE), the movable stator is not balanced in a hydrostatic way with the work forces of the fluid and its decentralisation can only be obtained by means of a strong system of levers, resulting in an excessive and heavy obstruction.
The command system is a complication of hydrostatic valves which are in their turn connected to a complication of hydrostatic cylinders of fluid supply.
Besides, there is not a direct automatism between the variation of the fluid pressure in the main hydrostatic circuit, which results from the variation of the work load and the debit variation of the said fluid.
This kind of hydrostatic transmission, which must be equipped with complicated and large performance and control devices and which do not possess a direct automation, cannot have an easy practical application.
It is obvious that they do not have anything similar to the simplification and lightness of the control devices and to the direct automatism, which are fundamental characteristics of the present and new invention.
In the new invention, one piston only direct supplied by the fluid pressure of the proper transmission circuit and in co-operation with a simple system of laminar springs, performs automatically the variation of the stator decentralisation, which results in the direct obtaining of the variation of the fluid debit in correspondence with the variation of the work load of the transmission.
The considerations previously stated can be applicable in relation, to the transmission type described in the Document U.S. Pat. No. 3,890,787 A (VAUSON WARREN C) and in the following documents:
GB 992 587 A (VEB INDUSTRIEWERKE KARL-MARK-STADT:
U.S. Pat. No. 3,959,969 (TITTMANN EGON ET AL);
U.S. Pat. No. 3,808,814 A (MACY R).
The invention refers to control devices applied in a hydrostatic transmission, which includes a motor pump MP, a hydrostatic circuit HC 1 and HC 2, and an impelling pump IP, which is formed by a rotor 1, a stator 2 and a body 3; the fluid debit is infinitely variable and is obtained by the radial and variable decentralisation of the said stator 2, by means of the impulsion of the rods A and B.
The devices are constituted by pistons 4 and 5, which impel the rods A and B, and are inserted in cylinders 6 and 7; by springs systems 9, 10 and 11, which regulate the position of the pistons and of the rods, and by a command formed by a valve 8, inserted in a vacuum circuit with ways V1 and V2, which communicate with the cylinder 7.
Through way V1 the vacuum effect acts on the piston 5, obtaining the decentralisation of the stator 2 in direction of the rod A; the fluid pressure transmitted by the extension HE to the piston 4, regulates the debit of the impelling pump and the rotation speed of the motor pump, whose rotation direction is the same as the impelling pump, FIG. 1.
Through way V2 the decentralisation of the stator 2 is obtained in the inverse direction to the rod A, and the rotation direction of the motor pump is inverse of the rotation direction of the impelling pump, FIG. 2.
When the command is not activated, no fluid impulsion is transmitted by the impelling pump and there is no rotation of the motor pump, FIG. 3.
Due to the fundamental characteristics of compensation and balance of the external and internal pressures to the movable stator 2, the basic purposes of the invention are: to reduce the number of control devices and to simplify their shape in order to obtain an insignificant obstruction; to optimize their functioning in order to obtain a direct decentralization variation of the stator and the corresponding automatic variation of the fluid debit in correspondence with the variation of work load of the transmission.
In a previous application, we developed a hydrostatic pump IP, of infinitely variable debit, which includes a rotor 1, a stator 2 and a body 3; the infinitely variable debit is obtained by the radial and variable decentralisation of the said stator by means of the impulsion of the rods, A and B.
The different work pressures of the fluid, which act on each internal side of the stator, are compensated and balanced on the corresponding external side by equal fluid pressures transmitted to chambers; each one of the said chambers is contiguous to each one of the sides.
A great advantage of the application of this method is that the strength applied in the impulsion of the rods is small and independent from the work pressures of the fluid; this fact permits the application of the adequate devices, in order to obtain an easy and safe control of the variation of the amplitude and of the direction of the decentralization of the stator of a hydrostatic pump, either its function is impelling or motor.
The said control devices of a hydrostatic transmission are constituted by pistons 4 and 5, which give impulse to the rods A and B and are inserted in cylinders 6 and 7; by systems of springs 9, 10 and 11, which regulate the position of the pistons and of the rods; and by a transmission control formed by a valve 8, inserted in a vacuum circuit with two ways V1 and V2, which communicate with the second cylinder 7.
The application and the functioning of the said devices, are explained below with the help of the description of three illustrative examples, and without a limited character, of the conception and application of the said devices, which perform the present invention in the preferred form.